Hmm. This seems more than a tad bit challenging. Remember that there aren't that many people on this site, it's optimistic to think that ten people will join. Now even with ten people joining that leaves roughly two people per faction and character interaction is a big thing in RP's, without it people loose interest quickly and the RP will die. With just two people per faction, interaction would be low and people are more liable to loose interest. On top of that the plot, I'm assuming, would be that all the factions are trying to undermine each other and rule the Mojave for themselves. This is hard to pull off in practice just because of how large and non-linear that goal and may end with a lot of people not knowing what to do and thus a lost of interest.
I would suggest cutting the number of factions to one or two for starters. This is just my humble opinion, however, and anything is possible.